2
Adaptive Site Management

MOTIVATION FOR ADAPTIVE SITE MANAGEMENT

The Navy’s request for guidance on its environmental cleanup program was prompted in part by the ineffectiveness of current remedies to meet cleanup goals at their major remaining hazardous waste sites, particularly those high-risk sites contaminated with recalcitrant chlorinated solvents and metals, often in complex hydrogeologic or sediment settings. Remediating and reaching closure for these types of sites has proved to be elusive in the context of current technologies. In addition to the ineffectiveness of many remedies, the Navy is also struggling with how to balance and meet different remediation goals, such as risk reduction, attainment of drinking water standards, and complete removal of the source of contamination. This chapter first explores these two basic problems (the multiobjective nature of cleanup and the ineffectiveness of current remedies to meet cleanup goals) and then introduces adaptive site management—an approach that can address these problems while encompassing all stages of cleanup.

Multiobjective Nature of Site Cleanup

Contaminated sites can pose multiple hazards to human and ecological health, natural resources, and the economic and social welfare of surrounding communities. In a similar vein, the objectives for site cleanup and restoration are multidimensional and often evolve over time. The eight key objectives are:

  1. To protect the health and safety of those on the site and in surrounding communities,



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2 Adaptive Site Management MOTIVATION FOR ADAPTIVE SITE MANAGEMENT The Navy’s request for guidance on its environmental cleanup program was prompted in part by the ineffectiveness of current remedies to meet cleanup goals at their major remaining hazardous waste sites, particularly those high-risk sites contaminated with recalcitrant chlorinated solvents and metals, often in complex hydrogeologic or sediment settings. Remediating and reaching closure for these types of sites has proved to be elusive in the context of current technologies. In addition to the ineffectiveness of many remedies, the Navy is also struggling with how to balance and meet different remediation goals, such as risk reduction, attainment of drinking water standards, and complete removal of the source of contamination. This chapter first explores these two basic problems (the multiobjective nature of cleanup and the ineffectiveness of current remedies to meet cleanup goals) and then introduces adaptive site management—an approach that can address these problems while encompassing all stages of cleanup. Multiobjective Nature of Site Cleanup Contaminated sites can pose multiple hazards to human and ecological health, natural resources, and the economic and social welfare of surrounding communities. In a similar vein, the objectives for site cleanup and restoration are multidimensional and often evolve over time. The eight key objectives are: To protect the health and safety of those on the site and in surrounding communities,

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To ensure the ecological viability and health of native plants and animals, and migratory species, To protect and restore natural land and water resources, To promote positive economic value and development in the area of the site, To comply with all applicable laws and regulations governing the site and the cleanup process, To promote positive participation and communication with the local community and other affected stakeholders, To advance the understanding of site contamination and cleanup processes (technical, managerial and social), and To accomplish each of these objectives in an affordable, cost-effective, and efficient manner. These objectives are usually pursued with different emphasis and urgency in different phases of a site cleanup effort. Following site discovery, the first priority is to eliminate immediate threats to human health and safety. Open contamination is enclosed, leaks are plugged, and, if necessary, local residents are switched to alternative sources of drinking water and other protective measures are implemented. Similarly, acute risks to wildlife and aquatic species are controlled to eliminate fish kills, animal poisonings, and other effects that could threaten the viability of ecosystem populations on or near the site. Virtually all Department of Defense (DoD) and other federal sites in the United States have passed beyond this initial phase of site discovery and “emergency response.” Following the control of immediate site hazards, cleanup and management can emphasize different remediation goals and objectives. A broad range of operational objectives have evolved over the last 20 years, from complete soil, aquifer, or sediment restoration to use of a technology-based approach to goals based on minimizing long-term risk to humans and the environment (“risk-based” objectives). The objectives listed above are closely related to the set of nine criteria established in the National Contingency Plan (NCP) for the evaluation of a proposed remediation plan.1 Thus, for example, the first NCP criterion of overall protection of human health and the environment is 1   The NCP criteria (EPA, 1990) include (1) overall protection of human health and the environment; (2) compliance with the chemical-specific standards that are considered the statutorily required “applicable or relevant and appropriate requirements” (ARARs); (3) long-term effectiveness and permanence; (4) reduction of toxicity, mobility, or volume through the use of treatment; (5) short-term effectiveness; (6) implementability; (7) cost; (8) state acceptance, and; (9) community acceptance.

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divided into two separate objectives—one for human health (objective 1 above) and one for ecosystem protection (objective 2 above)—because the steps needed to pursue these objectives are not always fully coincident. The NCP criterion for compliance with the chemical-specific standards that are considered the statutorily required “applicable or relevant and appropriate requirements” (ARARs) is equivalent to this report’s fifth objective for regulatory compliance with Superfund and applicable state requirements. For contaminants in groundwater, a typical ARAR would be the maximum contaminant level (MCL) for that compound, if one exists. Some states may adopt a “complete restoration” and thus more stringent goal as the site-specific cleanup objective, with which the Navy would need to comply. Superfund and some state regulatory programs allow nonresidential land use assumptions to be considered in the selection of cleanup levels and remedies, so long as selected remedies are protective of human health and the environment. The three NCP criteria of long-term effectiveness and permanence, short-term effectiveness, and implementability are not specifically noted in the list on page 2 because these features of a remediation plan are all essential to ensure that the other objectives are met. Similarly, reduction of toxicity, mobility, or volume through the use of treatment is the operational objective of a site cleanup needed to accomplish the broader objectives, and is addressed in a subsequent discussion. The seventh NCP criterion regarding cost is equivalent to this report’s eighth and final objective, because it constrains the extent to which all other objectives can be met. Cost minimization is a key objective in any public or private endeavor, although the weight placed on cost depends on the relevant statute and site-specific factors (EPA, 1996a, 1997a). Given the long-term requirements of site cleanup and stewardship at many sites, estimating costs over the full life cycle of a project is difficult. Approaches that appear cost-effective because of lower capital and initial operating costs may in the long term be more costly, especially if unanticipated problems arise in remediation performance and/or site conditions. Better anticipation of such problems, both initially and through ongoing data collection and evaluation, and ensuring that flexibility is maintained for improving or changing remediation technologies when needed, are key elements of the adaptive site management approach proposed later in this chapter. As discussed in the recent Guidance for Optimizing Remedial Action Operation (RAO) report for the Navy (NAVFAC, 2001), careful assessment of operation and maintenance costs for site cleanup plans can reveal many opportunities for cost

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reduction (see Box 2-1). The eighth and ninth criteria of the NCP (state acceptance and community acceptance) are related to this report’s fifth objective for regulatory compliance and sixth objective for positive participation and communication with the local community and other affected stakeholders. Positive participation includes community involvement in the development of remediation proposals rather than implying (as “community acceptance” does) that the community be involved only after remedial plans are proposed. As recognized by EPA (1999a, 2000a), effective public participation and input into the planning of a site cleanup are both a means—to ensure that the remediation plan can be implemented without costly delays and conflict—and an end—because public participation is a core value of a democratic society. Promoting participation and communication with the local community and other affected stakeholders applies to all aspects of a military site’s operation, but it is especially important in dealing with health and safety risks to the public, where trust is easy to lose, but very difficult to regain (Slovic, 1993). BOX 2-1 Important Elements of Long-Term Site Remediation Operation and Maintenance Costs, and Opportunities for Reducing These Costs (from NAVFAC, 2001, Table 6-1) Labor—Labor costs can be minimized through the use of remote and automated data-acquisition systems; the use of base personnel for routine operation and maintenance; and the contracting of the operation and maintenance for similar systems in bulk packages, achieving economies of scale and reducing administrative burden. Analytical Costs—Long-term, frequent, and spatially extensive analysis of many chemical and biological parameters is expensive, but can be reduced by focusing on data needed to track remediation effectiveness; by using onsite analyses for measurements taken frequently; by seeking bulk analysis discounts for coordinated sampling events; and by reducing regulatory sampling frequencies if compliance is demonstrated on a consistent basis. Power/Utilities—Energy and utility efficiency can be improved by the proper sizing of equipment; the use of periodic, pulse modes for in situ operations; and creative, onsite use of treated water for cooling water, landscaping, fire response supply, etc. (thereby reducing the need for purchasing such supplies). Repairs—System repair costs can be controlled by using standardized system designs with common replacement parts and by maintaining careful records to ensure full use of vendor warranties.

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Our list of objectives includes three that are not explicitly mentioned in the NCP remedy criteria: to protect and restore natural land and water resources (objective 3 above), to promote positive economic value and development in the area of the site (objective 4 above), and to advance site-specific and more general scientific knowledge (objective 7 above). The inclusion of objectives 3 and 4 is based on the fundamental importance of these issues in environmental and economic policy and on the committee’s professional experience as to what is important to states and communities. These objectives are especially likely to arise as a key component of long-term site stewardship and management efforts, once the more immediate threats to health and safety are addressed. The restoration of land and water resources and the return of economic value may or may not be linked for a given site. For some uses, ensuring that there are no (or minimal) risks to health and safety may be sufficient to allow surrounding economic development (including use of lands for recreational or species preservation purposes, if this is the locally targeted objective) to proceed, even though some land and water (especially groundwater) contamination remains. In other locations, planned uses may dictate a more complete cleanup. When site cleanup is critical to an economic or community development plan for a region, strong community and political pressure will be brought to bear both to identify cleanup criteria that can be met in a timely manner and to proceed with the needed effort to reach this objective. Our seventh objective of advancing knowledge during a site cleanup effort—both knowledge of the site itself and broader insights applicable to other sites—is usually secondary, and as a practical matter may be hard to justify to site managers and the public alike. However, because the science of cleaning up hazardous waste sites is often insufficient to attain even risk-based remediation goals, advancing scientific knowledge must be a component of site remediation. That is, such learning is essential if the other cleanup objectives are to be met in an effective manner. Although scientific study cannot be the principal driver for site cleanup (taking precedence over essential health, safety, and economic objectives), failure to take advantage of opportunities to use data and experiences acquired as part of a cleanup program to enlighten and guide subsequent efforts is in itself wasteful and dooms many of these later efforts to repeat mistakes that could otherwise have been avoided. Indeed, for responsible parties with large numbers of hazardous waste sites, the benefits that accrue from scientific study can be captured by using what is learned in one place at other sites and in future decisions. More focused and explicit building, cataloging, and transmission of knowledge

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during remedial investigation, remedy implementation, and monitoring is a key feature of the proposed adaptive site management process. Given the close correspondence and dependence of the objectives put forth here with those identified in the NCP for remedial selection, the Navy and other agencies can view this charge for ongoing management as fully consistent with the existing directives and goals. Risk Reduction Versus Mass Removal Objectives The eight broad objectives discussed above can help guide the overall context and goals of a site remediation plan. However, it can be difficult to translate these into specific programs and activities for site cleanup (especially all at once). To assist in this effort, two more specific site cleanup metrics, contaminant mass removal and risk reduction, are often used to define the specific operational objectives of a remediation program. Like the eight broader objectives identified above, these two metrics are consistent with previous NCP guidelines (i.e., for the reduction of toxicity, mobility, or volume) and with well-established procedures already used by the military and other federal agencies to track and evaluate cleanup. These specific operational objectives can promote the broader goals of site cleanup to different degrees. For example, contaminant mass reduction may (in some cases) be especially important for achieving objectives 3 and 4 (natural resource protection and economic development), with risk reduction being central to the first two objectives (protecting human and ecological health and safety). Evaluating the potential for risk reduction—central to a risk-based approach to site cleanup—has been used with increasing frequency in recent years. This approach defines the objectives for site cleanup as solely, or at least principally, to minimize human health and/or ecological risk (NRC, 1999a). Although socioeconomic impacts and risks to community welfare are sometimes considered in a broader framing of risk issues, they are rarely included in a formal risk assessment.2 Depending on the current or potential hazard to human and/or ecological health and safety, a risk-based approach may lead to full-scale remedial activities (e.g., complete removal of the contaminant source); to more limited onsite engineering and control activities (e.g., containment measures); or 2   See NRC (1996) pp. 45–47 for a discussion of socioeconomic and community-welfare risks, including effects on property values, increased community emergency preparedness costs and insurance premiums, community stigma and disruption, and concerns for environmental justice and equity.

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even to no onsite remediation (e.g., use restrictions and other institutional controls). Thus, risk-based approaches as defined do not place inherent value in soil and groundwater resources, unless human or ecological health is directly threatened by contamination of those resources. As a consequence, risk-based approaches are more likely than strategies aimed at natural resource restoration to result in remedies that leave contamination in place. Box 2-2 describes risk-based approaches, which have gained growing acceptance as a basis for site management decisions despite controversy surrounding the risk assessment process. As noted in the box, a broader definition of risk, combined with effective community input and communication, can help to ensure that risk assessments are appropriately structured and implemented to include the key values and concerns of the affected parties at a site. Although risk reduction at a site is always sought, source removal (also called mass removal) at the site can be an objective in and of itself. This is because a site that contains significant quantities of remnant contamination may require continued limitations on human use or ecological function, leading to a loss of natural resource value and economic benefit. Surrounding property values and local or regional development may be impaired by the presence and stigma of remaining contamination and perceived risks, even if the actual risks of exposure have been minimized (e.g., Edelstein, 1988; Zeiss and Atwater, 1991; Gregory et al., 1995). Furthermore, breaches of the containment or loss of institutional controls could lead to actual exposures and risks for future generations. It is sometimes the case that technologies that achieve some (or even a high degree of) mass removal may have little effect on exposure concentrations. Aggressive mass removal can even lead to increased pollutant release and mobilization in the surrounding environment, at least for the short term. This concern is especially important when considering large-scale excavation of contaminated soils or active dredging of sediments. Although risk reduction and mass removal are not the only targets for hazardous waste cleanup, they are common operational objectives; thus, their relationship is explored in greater detail. There are distinct tradeoffs between different treatment strategies in terms of meeting mass removal and risk reduction goals of cleanup over time. Figure 2-1 schematically shows both the contaminant mass removal (A) and the exposure or potential risk (B) using alternative cleanup and management methods over time. Two major types of remediation strategies are illustrated in Figure 2-1. The first type, designated as an “M” strategy, seeks

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BOX 2-2 Risk Reduction as a Basis for Site Management A focus on risk reduction for site management implies that the presence of contaminants onsite or in a specific medium does not necessarily constitute unacceptable risk when exposure occurs at a level below which potential harm can occur. Thus, actions are focused on alleviating or reducing risks and not necessarily on full source mass removal (although it may be that removal is one of the risk management actions taken). On an historic level, risk assessment was developed to provide some quantitative measure of potential harm and was considered essential to developing a practical cleanup program (GAO, 2000). There is sometimes opposition from environmental groups and affected residents over the use of a risk-based approach to cleanup versus one that stresses complete cleanup to natural or background levels. Critics argue that risk assessment is a tool that can be easily manipulated (Woodhouse, 1995; Andrews, 1997; Sexton, 1999; O’Brien, 2000). In its worst application, some say it is used to justify a specific, preferred (usually less costly) action, such as leaving in place large amounts of contaminants in soils or sediments. Risk-based approaches may appear to be biased or arbitrary to some, because the same data may be viewed, interpreted, and applied differently by different scientists, and the nonscientist often may not have a sufficient background to choose between “dueling” experts. Similarly, there are few black and white decisions in the “manage the risk approach,” whereas in the mass removal approach, the decision could be relatively straightforward—“remove a certain percentage of the mass.” There are important benefits that accrue with a risk-based approach, so long as it is broadly defined to include the full range of important human health, ecological, and socioeconomic impacts. First, a risk-based approach gives the decision maker the ability to prioritize areas for action so that the most important or high-risk areas are addressed first. Being able to prioritize also equates to a more efficient and timely use of funds. More important, if the approach were simply based on mass removal, some actions may be taken that lead to no concrete improvements in human health, the environment, or community welfare. The risk-based approach uses data to help guide the risk management action. Once such actions are implemented, scientists have an established mathematical basis and a database on which to build a monitoring plan to ensure that these actions have the intended result. A complicating factor in the risk-based approach is public perception. Often it can be difficult for scientists and decision makers to explain readily (or clearly) why leaving contaminants in place does not pose an unacceptable risk to human health or the environment. This difficulty feeds public skepticism, and the risk-based decision may face great difficulty in being accepted (see, for example, NRC, 1989; Kasperson et al., 1992; Renn, 1999). It can be much easier to convey the objective of mass removal than to convey the scientific reasons for leaving contaminants in place. Despite these limitations, the risk-based approach to environmental decision making has developed considerably over the last ten years, for situations in which both humans and ecological receptors are affected (Pittinger et al., 1998; NRC, 1999a; Sexton, 1999; Stahl et al., 1999, 2001).

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FIGURE 2-1 Two representations of the same cleanup situation. (A) shows the amount of contaminant mass remaining at a site as cleanup progresses, while (B) shows the amount of exposure or potential risk for the same cleanup plan. M strategies emphasize contaminant mass removal, while E strategies focus on exposure and risk reduction. The question mark refers to the possibility that onsite containment or an institutional control fails, leading to a sudden increase in exposure and potential risk.

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first to remove contaminant mass. M1 represents an in situ mass removal strategy, which is typified by an asymptotically diminishing capture, since the last portions of remaining mass are often difficult to access and remove and may thus remain in place (Figure 2-1A). As shown in Figure 2-1B, M1 also displays a limited reduction in exposure concentrations and potential risk until a significant portion of the onsite mass is removed. The M1 curve represents the known behavior of certain in situ technologies, such as chemical oxidation or active bioremediation. Vapor extraction and conventional pump-and-treat might also yield results of this type of curve in the case where much (even if not all) of the pollutant mass is found in, or is readily transferred to, the captured fluid. Strategy M2 represents a more aggressive mass removal strategy, such as soil excavation or sediment dredging, which achieves results over a shorter time period (Figure 2-1A) but which might lead to short-term increases in exposure and risk during the period of implementation (Figure 2-1B). The second type of remediation strategy, indicated with an “E,” places first priority on reducing exposure to contamination. E1 represents an approach like plume containment, reactive barrier walls, or natural attenuation where the contaminant source zone is not targeted and the focus is on exposure reduction at some compliance point. E2 represents a pathway intervention strategy that would be implemented through institutional controls or onsite containment leaving the bulk of the contamination in place. The dotted upward arrow for E2 in Figure 2-1B signifies the possibility that the remaining onsite contamination could become exposed and impose a potential risk in the future, if the containment is breached or the institutional control is lost. Figure 2-2 combines the progress in mass removal and risk reduction into a single, multiobjective graph. With this representation, the origin represents the starting point of site cleanup, when there is significant contaminant mass present at the site and affected populations are subject to significant exposure and potential risk. Progress in achieving cleanup and restoration is shown by moving along one of the paths over time toward the upper right-hand corner (i.e., total risk reduction and complete mass removal). Although the ultimate goal of cleanup and restoration is to move to this point in as rapid and efficient a manner as possible, this is not always feasible. Indeed, in many cases the costs are prohibitive, and the objectives of complete mass removal and/or exposure and risk elimination may simply be unachievable with current technology and policy options. As discussed in Chapter 3, visualizations like Figures 2-1 and 2-2

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FIGURE 2-2 A multiobjective representation of alternative remediation and site management strategies in terms of contaminant mass removal and exposure or risk reduction. This graph combines Figures 2-1 A and B. The question mark refers to the possibility that containment or an institutional control fails, leading to a sudden change in exposure and potential risk. can be used as a means for assessing and tracking the effectiveness of facility management options as a program for site restoration and stewardship evolves over time. By collecting the data and information necessary to record progress to date and by predicting (using mathematical models) the possible future outcomes for the objectives displayed in these figures, a more coherent and responsive effort can be planned and executed for the adaptive site management program recommended in this study. Effectiveness of Remedies Adaptive site management is needed not only to handle multiple and sometimes conflicting objectives, but also to provide flexibility when

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uncertainty in system response. Given this, and the strong support for adaptive approaches already present in recent federal guidance on monitoring and remediation, we propose adopting ASM for site cleanup and long-term stewardship. ASM is an iterative, flexible approach to improving federal site cleanup. It builds on recently developed guidance for the Navy (NAVFAC, 2001), but provides a much broader and more well-defined series of tasks to ensure that remediation is cost-effective. Whereas the recent Navy guidance also recommends close scrutiny of existing remedies and monitoring data, ASM goes further to suggest how to interpret the monitoring data, when to consider using new technologies, and how to reach site closure for all types of sites. The differences between current cleanup practice and ASM with regard to monitoring and data analysis, evaluation and experimentation, and long-term stewardship are elaborated in Chapters 3, 4, and 6, respectively. A critical aspect of ASM is its call for evaluation and experimentation, and the coupling of that information with the adaptation of remedial programs so that ineffective or inefficient remedies are replaced quickly. This approach presents a way to manage uncertainty while moving forward with the cleanup process because conventional remedies can be implemented first while additional information is being gained on innovative but more risky technologies. ASM formalizes discrete management decision periods to provide an explicit mechanism for communication (between the RPM and remediation team, the regulatory agencies, and interested stakeholders), to allow for critical evaluation of information, and to guide the determination of new management actions. MDP1 ensures that a selected remedy is indeed the right one to implement, while MDP2 details how to assess remedy effectiveness based on monitoring data. MDP3 draws upon monitoring data as well as information from evaluation and experimentation and stakeholder input to optimize, modify, or replace remedies or revise remedial goals. MDP4 provides the road map for long-term stewardship and site closure for sites where residual contamination remains in place. In addition, MDP4 suggests how to make forward progress at sites where remedies, such as pump-and-treat systems and monitored natural attenuation, require substantial financial resources for monitoring, operation, and maintenance. Feedback loops are present throughout in order to revisit different points when new information warrants such an examination. A final important feature of ASM is its applicability to sites at any stage of cleanup. There is little more than anecdotal evidence about the difficulty or

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ease which with remedies can be changed, although it is likely that there are disincentives for RPMs to optimize or change in-place remedies in some cases. ASM institutionalizes the concept of being open-minded about chosen remedies, and its success will depend on the creation of incentives to promote this mindset. The recent trend within the Navy of optimizing existing remedies and changing ineffective remedies, but without the benefit of evaluation and experimentation (see example in Box 2-7), suggests that the Navy and other federal agencies would have a need for and an interest in ASM. Given its many discrete decision points and the evaluation and experimentation track, it is possible that ASM will be time-consuming and (over the short-term) more expensive than the current practice. Thus, full-scale ASM that includes public participation during all decision periods should be targeted to the more complex (e.g., multiple contaminants and stressors, heterogeneous hydrogeology) and high-risk sites where projected large costs are at stake. An example would be where DNAPL contamination threatens a sole source aquifer. Indeed, these are the sites where cleanup goals are not being achieved and where innovative technologies are needed to provide new avenues for treatment. A substantial number of DoD sites, including Navy sites, fall into this high-risk/high-cost category. If targeted in this manner, the ASM approach is expected to lead to an optimum solution from both a cost and performance perspective, as well as to a solution acceptable to stakeholders. The benefits of ASM are expected to be less at smaller, low-risk, low-cost remediation sites (e.g., a BTEX spill at an UST site) where there is greater certainty about the ability of remedies to reach cleanup goals. Because of the enormous variability in site conditions across Navy facilities, it is not appropriate for this report to suggest a distinct cost basis for assessing whether or not to use ASM—for example, transactional costs should only represent a certain percentage of the total costs— although this may be possible in the future following more in-depth analysis by the Navy. Nonetheless, it is anticipated that up-front cost increases associated with implementing ASM will be balanced by the benefits of evaluation and experimentation, which include optimization of remedies and more expeditious achievement of cleanup goals. In many cases, the costs associated with ASM may be exceeded by the long-term savings that result from switching to a more efficient and effective technology or by overall life-cycle savings. These issues, along with pertinent examples, are discussed in greater detail in Chapters 4 and 6, respectively. Finally, current understanding within the military of what and for

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how long information needs to be collected, catalogued, and maintained is too inconsistent at present to fully support the ASM concept (M. Ierardi, Air Force Base Conversion Agency, personal communication, 2002). Information is currently found in many different information systems for records management, financial management, contract management, real-estate management, progress reporting, and technical data systems, most of which are not integrated. Greater understanding of the value of the information associated with the cleanup program will be needed to support ASM. Specific recommendations regarding data collection on remedy performance at federal facilities are discussed in Chapters 3, 4, and 5. The Navy and other federal agencies should adopt adaptive site management. To our knowledge, ASM has never been formally used for hazardous waste cleanup. ASM will enable site managers to use new data and innovative technologies when they become available, both during active implementation of remedies and during long-term stewardship. The Navy is currently drafting policy that will require periodic reviews of remedies, as prescribed by the recent NAVFAC (2001) guidance on optimization (R. Kratke, NFESC, personal communication, 2003). Because ASM is broader in scope than that guidance, it will be necessary for the federal agencies to develop guidance to further define the management decision periods that are inherent to ASM. Full-scale ASM that includes public participation during each decision period should be targeted to the more complex and high-risk sites where projected large costs are at stake. ASM is particularly appropriate for sites with multiple or recalcitrant contaminants and multiple stressors and heterogeneous hydrogeology because progress at such sites is likely to have stalled prior to reaching cleanup goals. Prior to widespread adoption, the Navy should consider pilot testing ASM at a limited number of high-risk, complex sites to allow Navy managers to better understand any transactional costs and delays that may accompany ASM implementation. REFERENCES Air Force. 2001. Final remedial process optimization handbook. Prepared for Air Force Center for Environmental Excellence, Technology Transfer Division, Brooks Air Force Base, San Antonio, Texas, and Defense Logistics

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BOX 2-7 Trend Toward ASM in the Navy A Navy site in Pensacola, Florida, was recently evaluated for the potential to reduce cleanup costs while maintaining or enhancing protectiveness by applying some of the principles of ASM (Navy, 2000). A TCE plume beneath a sludge drying bed had been undergoing remediation by pump-and-treat since 1987, using seven recovery wells. In 1995 the monitoring data were reviewed and indicated that the groundwater contamination had been reduced to Maximum Contaminant Levels (MCLs) at most of the site, although several high-concentration plume areas of 3,000–4,000 µg/L were present in the vicinity of monitoring well GM-66 (see Figure 2-8). Based on recovery well concentrations and in cooperation with the Florida Department of Environmental Protection, the Navy decided to reduce the number of recovery wells to three and to focus on reducing the high TCE concentrations near GM-66. In 1996 the monitoring data were reviewed again, and it was decided to discontinue pump and treat altogether and monitor for natural attenuation. In 1998 a program of in situ chemical oxidation was undertaken to address the removal of the high-concentration source areas. Fenton’s Reagent was used FIGURE 2-8 TCE plume delineation at Pensacola, FL, site. SOURCE: Navy (2000).

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as the oxidant in two phases of implementation, and ultimately a 97 percent reduction in chlorinated VOCs was achieved by early 2000 (see Figure 2-9). The latter data for well GM-66/66R indicate that the system may be showing a rebound effect in a portion of the domain. This trend should be monitored and assessed over time, with appropriate additional remedial action taken as needed. It was agreed that monitored natural attenuation would be used to reduce the remaining contaminant levels to MCLs. The Navy estimated that by implementing this alternative remediation scheme, a life-cycle cost savings of $2.56 million was achieved in monitoring and treatment, and this was accompanied by a reduction in cleanup time. This case study illustrates some facets of ASM because the original remedy was changed after assessing the results of remediation repeatedly over time. However, it is not clear what evaluation and experimentation activities were ongoing at the site during implementation of the original remedy and whether they may have formed the basis for the suggested changes. FIGURE 2-9 TCE levels resulting from in situ chemical oxidation at Pensacola, FL, site. SOURCE: Navy (2000).

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